1. Field of the Invention
The present invention relates to a conveying apparatus of the type including a plurality of driving means disposed in a spaced relation along a guide track so as to allow a carriage on the track to move under the influence of inertia with the aid of a propulsive force or reverse propulsive force which is generated by the plural driving means and more particularly to improvement of or relating to a conveying apparatus of the above-mentioned type which assures that the carriage moves along the curve of the track at a proper moving speed.
2. Description of the Prior Art
An example of conveying apparatus of the above mentioned type is a conveying system using linear induction motors. The conventional conveying system is typically constructed such that a carriage adapted to move along a track has a reaction plate fixedly secured thereto, a plurality of stators are disposed in a spaced relation along the track, magnetic flux which varies as time elapses is exerted on the reaction plate adapted to move past the stators and thereby a predetermined intensity of propulsive force or reverse propulsive force is generated on the reaction plate as magnetic flux varies so that the carriage moves on the track under the influence of inertia.
As is well known, moving efficiency of the carriage becomes deteriorated when a certain clearance fails to be maintained between the reaction plate and the stator and in practice it is usual that the clearance between the reaction plate and the stator is not kept constant when the carriage moves along the curved portion of the track. For this reason it becomes very complicated and difficult to control moving speed when the curve portion of the track is provided with stators. In view of the problem as mentioned above, the conventional conveying apparatus is normally designed such that stators are disposed at the position located just before the carriage enters the curve so as to allow the carriage to move past the curve under the effect of a sufficiently high intensity of propulsive force which is generated by means of the stators. However, due to the fact that centrifugal force is exerted on the carriage when it moves along the curved portion, the following problems have been pointed out.
(1) This type of conveying apparatus is often used for the purpose of conveying various articles but there is a fear of causing damage or injury on these articles under the effect of shock which is produced by centrifugal force.
(2) The surface along which the carriage comes in contact with the track has increased frictional pressure due to thus generated centrifugal force and this leads to generation of greatly increased noise compared with the case where the carriage moves on the straight portion of the track.
(3) Strength of the carriage and the curved portion of the track must be determined larger than that of the straight portion of the same in consideration of the effect of centrifugal force when the carriage moves along the curved portion.
As another prior art, Japanese Laid-Open Patent No. 119616/1980 discloses a system which includes a common rail extending between an accounting room and a plurality of cashier booths in the bank and a carriage on which cash, bills or the like are placed, wherein weight and moving speed of the carriage are detected and an extent of controlling required for stopping the carriage is determined in dependence on thus detected weight and moving speed. However, it has been found that this conventional system has such a problem that precise and reliable controlling cannot be achieved when the carrier moves along the curved portion of the rail because the system takes into account only weight and moving speed of the carriage.